This class inherits from the missing_data.frame-class but is customized for the situation
where the sample has a multilevel structure.
Objects can be created by calls of the form new("multilevel_missing_data.frame", ...).
However, its users almost always will pass a data.frame to the
missing_data.frame function and specify the subclass and groups arguments.
The multilevel_missing_data.frame class inherits from the missing_data.frame-class and
has two additional slots
Object of class character indicating which variables define the
multilevel structure
Object of class mdf_list whose elements contain a missing_data.frame
for each group. This slot is filled automatically by the initialize method.
Ben Goodrich and Jonathan Kropko, for this version, based on earlier versions written by Yu-Sung Su, Masanao Yajima, Maria Grazia Pittau, Jennifer Hill, and Andrew Gelman.
The fit_model-methods for the multilevel_missing_data.frame class will, by default, utilize
multilevel modeling techniques that shrink the estimated parameters for each group toward their global
means.
missing_data.frame